C-di-GMP signaling

Intro
The cyclic dinucleotide c-di-GMP is a second messenger that mediates the regulation of cell sur- face associated traits in bacteria. The regulatory network includes and
 * GGDEF and EAL domain proteins that catalyze c-di-GMP synthesis and degradation, respectively (and thereby control the cellular c-di-GMP level)
 * PlzD domains as part of down-stream c-di-GMP receptors.

Diguanylate cyclases
The condensation reaction 2 GTP -> c-di-GMP + 2 PPi is catalyzed by GGDEF domains that typically occur in combination with sensory or regulator domains. The structures of two diguanylate cyclases (PleD and WspR) have been determined, both being response regulators with a response regulator receiver (Rec) and a GGDEF output (effector) domain. Response regulators are activated through phosphorylation of a conserved aspartate by cognate histidine kinases.

C-di-GMP specific phosphodiesterases
Cleavage of one of the phosphodiester bonds is catalyzed by EAL and HD-GYP domains. Thereby, the cylic dinucleotide c-di-GMP is converted to the linear pGpG form. Two structures of EAL domain proteins have been determined in complex with substrate c-di-GMP (YkuI 2w27 and BlrP1 3gg0) and are presented here.